Photoluminescent marking of egress pathways has gained importance over the past ten years. This is the result of both the advent of high performance, long afterglow strontium aluminate pigments, and the recognition of the need for illuminated pathway markings in emergency, blackout conditions. In densely populated buildings, increasing safety cues can result in less hesitation during emergency exits. For these reasons, it is becoming common to require that emergency exits be marked with photoluminescent guidance systems. An example of a photoluminescent guidance sign is shown in U.S. Pat. No. 6,487,802.
Guidance cues can be provided by marking the edges of the egress pathway. This is usually done low to the ground, as in many emergencies there is the presence of smoke, and combustion by products, which rise due to heat. As a result the clearest view is of the lowest portions of a pathway. For this reason the optimum placement of egress markings is on either the floor, or the lowest portion of the wall. An example of this type of product is shown in U.S. Pat. No. 5,904,017, where a photoluminescent strip is extruded into a floor molding, or other attachable material.
Commercial, long afterglow photoluminescent signs, markers, and tapes are usually compounded from strontium aluminate pigments. Other pigments, such as zinc sulfide can also be used, however the performance isn't quite as long lasting. All of the pigments behave in the same general way by absorbing ultraviolet (UV) light radiation and discharging visible light. When the UV light source is removed, the afterglow of visible light discharge continues for some time, although it does decay eventually. The useful life of a photoluminescent sign, during a blackout, is dependant on this property. Without sufficient UV light to charge the sign, the afterglow is limited.
Emergency exits of many buildings are illuminated by fluorescent lighting. Fluorescent lighting works by the internal UV discharge causing the fluorescent coated layer to charge and give off visible light. This effect is not photoluminescent, because as soon as the UV charging is removed, the fluorescence ceases. The output of a fluorescent lamp is primarily visible light, however a small percentage of the UV light is emitted through the coated layer and the glass. This allows a fluorescent lamp to be used as a source for charging photoluminescent signs, markers, and tapes. While illumination levels in an office space may be high, to allow for efficient operations, illumination levels in emergency exit pathways is kept to a much lower level for energy efficiency. This level varies, depending upon the building code in effect and the building owner's preference. In one large metropolitan city, the minimum level can be as low as 2 foot-candles. Making the most efficient use of the illumination provided is an important factor in providing the most conspicuous egress marking.
Photoluminescent egress marking can be applied to the floor, providing a photoluminescent surface that is nearly perpendicular to overhead illumination and, depending upon observer position and height, at a close to perpendicular angle to viewing as well. This generally results in both good illumination of the photoluminescent tape as well as good, viewable brightness of the marker luminance in black-out conditions.
Sometimes the egress marking cannot be applied to the floor, either due to a difficult to bond surface, difficulty in cleaning or otherwise preparing the surface for bonding, or other obstacles. In this case the marking is applied along the lower portion of the wall, near the floor. If a flat tape-like material is used, with its photoluminescent surface parallel to the wall, the tape is at an acute angle to both illumination from overhead lighting and observation by an upright viewer. This angle can diminish the effectiveness of the marking and slow recognition by the viewer in a black-out, emergency situation.
A solution to the problem of the performance of wall mounted photoluminescent markings is to mount the marking at an angle to the wall. The greater the angle, the more illumination will be provided to it by the overhead lighting and the more observable it will be in a black-out by an upright viewer. This has been recognized by some providers of photoluminescent wall markings in the form of an angled mount for a photoluminescent tape or insert to be applied to. Angled mounts can be manufactured from either stamped or extruded metal or plastic.
The disadvantage of the current angled mounts is that they must be made in rigid lengths. Providing the angle feature requires the mount to have a significant third dimension, which adds greatly to its longitudinal stiffniess. This means that the length of the mounts is restricted to the greatest length that can be efficiently made, stored, transported, and installed. Even eight foot lengths present a challenge for convenient handling, especially when being transported up emergency exits on multi-story buildings. Flat tapes and flat mounts for tapes and markings can be provided and dispensed from convenient rolls in much greater lengths, but do not supply the angled display feature. Accordingly, a need exists for an effective photoluminescent wall marker that can be efficiently stored and transported.